The production of hollow rubber bladders, such as those used to produce basketballs and the like, is currently a rather complex process. Rubber compounds, usually butyl rubber, are compounded at high energy consumption on a rubber mill or Banbury mixer. This compound is then calendered to the desired thickness in sheet form. From the rubber sheet, quarter sections of the bladder are die cut and pieced together by hand with adhesive and end patches. A valve is inserted and adhered into the construction. The total construction is then heat cured to produce a bladder. Because of the adhesive splices, which often form imperfect seals and poor weight balance, this conventional process often results in high amounts of defective bladders and excess scrap.
Rotocasting is a process now used to produce playballs from thermoplastic materials such as polyethylene powders and vinyl plastisols. Unfortunately, these materials do not have the resiliency and air retention of rubber and are not suitable for use in basketballs and the like.